The present invention relates to a discharge lamp suitable for a display fluorescent lamp as a display element such as an electrolight display board or the like for making compact the structure of the discharge lamp and improving symmetric property of light distributing characteristic.
One example of a conventional discharge lamp is shown in FIGS. 17 and 18. Referring to FIGS. 17 and 18, an illustrated discharge lamp comprises a bottomed lower cylindrical portion 301 made of ceramics and a bottomed upper cylindrical portion 302 also made of ceramics and mounted on the opened upper end portion of the lower cylindrical portion 301 coaxially therewith.
The interior of the upper cylindrical portion 302, as shown in FIG. 18, is divided into a plurality of, three in the illustration, luminous chambers 304a, 304b and 304c circumferential direction thereof, for example, by a Y-shaped partition wall 303, and the walls of the respective chambers 304a, 304b and 304c are coated with, for example, light emitting films of red color R, green color G and blue color B, respectively. The opened upper end portion of the upper cylindrical portion 302 is air-tightly sealed by a flat transparent glass plate 305 so as to constitute an air-tight tube 306.
The lower cylindrical portion 301 is provided with a central recess into which a common cathode 307 is sealed and with three circumferential recesses formed in the outer peripheral portions of the lower cylinder 301 into which anodes 308a, 308b and 308c are arranged in a manner corresponding to the luminous chambers 304a, 304b and 304c, respectively.
In the bottom portions of the respective luminous chambers 304a, 304b and 304c of the upper cylinder 302 are formed discharge holes 309a, 309b and 309c at the central portions of the chambers and discharge holes 310a, 310b and 310c at the outer peripheral portions of the chambers in a manner that the discharge caused between the cathode 307 and the anodes 308a, 308b and 308c pass these holes. Accordingly, when the cathode and the anodes are conducted and the discharge is caused between the cathode and desired one of anodes, the discharge passes corresponding one of the discharge holes into the corresponding one of the light emitting chambers, in which ultraviolet rays are generated and the light emitting film of the desired chamber is excited and lightened by the ultraviolet rays, whereby the light of the desired color is emitted outwardly through the transparent glass plate 305.
However, the conventional discharge lamp of the type described above, the upper and lower cylindrical portions are made of ceramics which have relatively thick walls and, hence, heavy weights. The ceramics cylindrical portions are inferior in the working performance and workability and in strength when the walls are made thin.
Furthermore, with a discharge lamp as a fluorescent lamp, there is a problem to be unavoidable such that a chromaticity of the white light at the time of all-chamber light emission deteriorates due to the asymmetric light distribution characteristic.